Local and global tests of models of soldier production in Pheidole ants

Colonies of ants of the genus Pheidole produce two discrete sterile worker castes, soldiers and minor workers. Naturally occurring colonies of Pheidole demonstrate great heterogeneity in the relative production of soldiers and minors. Some species have demonstrated the ability to adjust caste ratios in response to environmental conditions, but little is known about the interspecific patterns in caste ratio at local and global scales, nor about the demographic and morphometric parameters among species that may affect the relative allocation among soldier and minor production. In this study we have extensively sampled entire colonies of twelve species of Pheidole from nineteen sites in a Costa Rican tropical rain forest to evaluate several competing models that potential may account for interspecific differences in soldier production. This experiment is augmented by complementary data on soldier production from prior studies from several biogeographic regions. We find that simple parameters regarding the biology of each species explain much of the interspecific variation in caste ratios.